virtio: rename dma helpers

virtio: rename dma helpers

Following patch will introduce virtio mapping function to avoid
abusing DMA API for device that doesn't do DMA. To ease the
introduction, this patch rename "dma" to "map" for the current dma
mapping helpers.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20250821064641.5025-4-jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Reviewed-by: Eugenio Pérez <eperezma@redhat.com>